The present invention generally relates to liquid metering pumps for delivering controlled amounts of liquid from one vessel to another, or from a source of supply to a process stream. More particularly, it relates to a new and improved effervescent gas bleeder apparatus for use on a liquid metering pump to prevent the metering pump from “air binding” or losing prime.
Diaphragm metering pumps are known and used for transferring fluids from one place to another. Generally, diaphragm pumps include a pumping head area including a product chamber bounded on one side by a displaceable diaphragm member. The inlet and exit to the product chamber are provided with one way check valves. As the diaphragm is displaced away from the product chamber, the exit check valve closes under reduced pressure, the inlet check valve opens and fluid is drawn into the product chamber. Thereafter, as the diaphragm is displaced toward the product side, pressure increases on the fluid in the product chamber, closing the inlet check valve, opening the outlet check valve and forcing fluid in the product chamber out of the exit. In continuous operation, a diaphragm pump pumps fluid through the product side in a pulsed manner.
Diaphragm displacements may be achieved with a mechanical drive system or a hydraulic drive system. An example of a mechanical drive is a solenoid-actuated pump. In a solenoid-actuated pump, an actuator rod is secured at one end to the diaphragm and at its opposed end is connected to a solenoid actuator. The electrically or electronically-controlled solenoid is effective to cause reciprocal linear movement of the actuator and actuator rod thereby causing displacements of the diaphragm directly. As an alternative, a mechanical drive system may include a motor, gearbox, and eccentric cam for driving the actuator rod.
In a hydraulically driven diaphragm metering pump, diaphragm displacement is achieved by varying the pressure of a hydraulic fluid on the hydraulic side of the diaphragm through operation of a reciprocating piston disposed in fluid communication with a hydraulic chamber. Instead of direct mechanical attachment to the diaphragm, with this type of pump, a hydraulic fluid is pressurized on one side of the diaphragm to cause diaphragm displacements toward or away from the product chamber. This also results in a pulsed pumping of a fluid through the pump head.
A problem which may arise in diaphragm metering pumps occurs during operation if a volume of air is sucked into the intake lines so that air travels through the suction line, or after sitting idle, gas accumulates in the pump head or in the suction line below the pump. Air or gas in the intake or pump head may cause the pump to lose prime. For effervescent fluids such as Sodium Hypochlorite and Hydrogen Peroxide, the reciprocating type pumps are very susceptible to “air binding” and losing prime. If the pump loses its prime and gas fills the diaphragm metering pump head area, pumping displacements of the diaphragm may simply compress the gas and not result in any liquid pumping or fluid flow. The compressibility of gases causes this effect. If there is a loss of priming, frequently a pump cannot regain hydraulic firmness and restart pumping.